The "Not Now" example looks disabled to my eye just as much as the disabled example.<p>I think the rule here makes sense as far as design works now, except that "Not Now" example.
I agree a cancel button should not be as prominent as the default button, but a greyed out button is terrible UX as it looks disabled.<p>Cancelling IS and action too.
A couple of years ago I accidentally cancelled my Adobe CC subscription because instead of being a fallback to safety as it normally is, the "Cancel" button immediately ended the non-refundable subscription[0]. I don't remember what the actual fallback to safety button was—probably "Now Now".<p>Adobe fixed that glaring problem soon after. I expect I wasn't the only one to make that mistake.<p>[0] You have to pay for whole year in advance and I was only one month in, which meant that was a $300 mistake. Fortunately, Adobe gave me a refund going through the rigaramorole of calling support, and they told me to create a new subscription. Which was great, because for some reason it gave me the one year student discount again, which I had already used the previous year.
We use Teams for video conferencing at work. When someone calls, there are three buttons. One of them, the hang up button, is red; the other two are blue. I hit the red one half the time. Maybe I'm not very smart, but it sure seems like it wants me to hit it!